WASHINGTON
— Call them the five horsemen of the Republican Revolution: incoming US Sens. Richard Burr of North Carolina, Tom Coburn of Oklahoma, Jim DeMint of South Carolina, John Thune of South Dakota, and David Vitter of Louisiana.

Their arrival in the US Senate next week gives a powerful boost to both fiscal and social conservatives on issues ranging from judicial nominations and abortion rights to tax reform. It also tips the number of former House members in the Senate to 52 percent - the first time it has passed a majority. More than just an additional five GOP votes, they bring a hard-driving style and ideological focus that is at odds with the collegial culture of the Senate.

"The big question is to what extent they will maintain their House attitudes and behavior ... and the uncompromising, disputatious positions that House members are likely to take," says Ross Baker, a political scientist at Rutgers University in New Jersey.

There's already speculation about how this group will interact with Republican colleagues, especially the moderates who often swayed key votes in the last Congress. They could transform the tone of an institution that has been tottering between its clubby past and the more disciplined, partisan style of the US House.

After a tour of the United States in 1831, French philosopher Alexis de Tocqueville summed up the difference between the House of Representatives and the Senate in a word: "vulgar." The Senate, he wrote in his classic "Democracy in America," "seems to enjoy a monopoly of intelligence and talent," while the House is remarkable for its "vulgar demeanor."

While no senator would draw so harsh a line today, Sen. Robert Byrd (D) of West Virginia came close, when in 1995 he chastised two Republican colleagues and former House members, for contributing to the "deterioration of the Senate" with invective and a "dangerous excess of party feeling."

That's why the arrival of these five former House members to the Senate next week is already stirring strong expectations, especially among conservatives.

"These five incoming Senators have been on the front lines of the Republican ideological revolution in the House. There's a high level of expectation for this class," says Michael Franc of the conservative Heritage Foundation.

A sixth former GOP House member, Rep. Johnny Isakson (R) of Georgia, is a pro-choice moderate with a record of working across the aisle.

While the House moved the Bush first-term agenda with discipline - and virtual exclusion of Democrats in key negotiations - Senate bills faced a tougher slog. Early on, Democrats and a handful of moderate Republicans joined forces against the high end of Bush tax cuts. And, in the face of Democratic filibuster threats, 60 votes became the effective threshold for passing major legislation or clearing judicial nominations.

With a 55-45 edge in the 109th Congress (counting Independent Sen. James Jeffords with the Democrats), Republicans have a better shot at moving the president's agenda. An early test will be judicial nominations. Last week, President Bush announced that he is renominating 20 judicial candidates who did not get a vote in the 108th Congress. Senate majority leader Bill Frist assigned Senator-elect Coburn and Sen. Sam Brownback (R) of Kansas, both strong opponents of abortion, to the Senate Judiciary Committee.

The Senate majority leader has also signaled that he may propose a rule to limit the minority's power to filibuster judicial nominations. While moderate Republicans have expressed doubts about this move, the GOP freshmen say they are open to supporting it.

The right to unlimited debate has been one of the defining differences between the House and Senate.

The new conservative senators will also boost GOP efforts to move legislation to cap medical malpractice lawsuits, as well as a constitutional amendment defining marriage as between a man and a woman.

Still, one of the most interesting flashpoints in the 109th Senate will be over tax reform and the soaring federal deficit. In his House days, Senator-elect Coburn was the terror, even to GOP leaders, over the issue of spending. In a protest over high levels of federal spending, Coburn piled on so many amendments to a 1998 agriculture appropriations bill that the process stalled for a year. Unlike some fiscal conservatives, he also voted against projects for his own district. He describes both abortion and the deficit as "a moral issue."

In his 2003 book, "Breach of Trust: How Washington Turns Outsiders Into Insiders," he blasts Republican congressional leaders for "folding" in budget fights and lapsing into careerism. "During meetings of the Republican conference it often seemed that the sole purpose for our existence was our own self-preservation," he writes.

In the Senate, such former House members will find greater capacity to bring the institution to a halt than in the House. After his election, Coburn told reporters that his goal is to "learn the rules as well as Robert Byrd."